Convert CONFIG_USE_BOOTCOMMAND et al to Kconfig

This converts the following to Kconfig:
   CONFIG_USE_BOOTCOMMAND
   CONFIG_BOOTCOMMAND
   CONFIG_RAMBOOTCOMMAND
   CONFIG_NFSBOOTCOMMAND

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/MPC8548CDS_legacy_defconfig b/configs/MPC8548CDS_legacy_defconfig
index 6584f67..45f007e 100644
--- a/configs/MPC8548CDS_legacy_defconfig
+++ b/configs/MPC8548CDS_legacy_defconfig
@@ -12,6 +12,8 @@
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_SYS_EXTRA_OPTIONS="LEGACY"
 CONFIG_BOOTDELAY=10
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="setenv bootargs root=/dev/nfs rw nfsroot=$serverip:$rootpath ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname:$netdev:off console=$consoledev,$baudrate $othbootargs;tftp $loadaddr $bootfile;tftp $fdtaddr $fdtfile;bootm $loadaddr - $fdtaddr"
 # CONFIG_MISC_INIT_R is not set
 CONFIG_ID_EEPROM=y
 CONFIG_HUSH_PARSER=y